Wind Power That Floats

Wind Power That Floats

Ocean bound: Since December, this prototype 80-kilowatt floating wind turbine has been absorbing wind energy off Puglia, Italy, in 108-meter-deep water, beyond the economically viable depth for turbines mounted on the seabed. Data from the machine’s interactions with wind and waves will inform the final design and control schemes for full-size floating turbines.

Offshore wind-farm developers would love to build in deep water more than 32 kilometers from shore, where stronger and steadier winds prevail and complaints about marred scenery are less likely. But building foundations to support wind turbines in water deeper than 20 meters is prohibitively expensive. Now, technology developers are stepping up work in floating turbines to make such farms feasible.

Several companies are on their way to demonstrating systems by borrowing heavily from oil and gas offshore platform technology. In December, the Dutch floating-turbine developer Blue H Technologies launched a test platform off Italy’s southern coast; last month, the company announced its plans to install an additional test turbine off the coast of Massachusetts, and possibly begin constructing a full wind farm off the Italian coast, next year. Close behind is SWAY, based in Bergen, Norway, which raised $29 million last fall and plans to field a prototype of its floating wind turbine in 2010.

The success of the floating turbine could hold the key to exploiting that resource. Wind farms such as those installed in Denmark, Germany, and other European waters and proposed for Nantucket Sound, in Massachusetts, suffer from a limited supply of marine construction equipment such as pile drivers and cranes. Emerging Energy Research, a consultancy based in Cambridge, MA, said last week that the global market for offshore wind energy could reach 40,000 megawatts by 2020–enough to power more than 30 million U.S. homes, and more than twice the scale of last year’s wind installations worldwide–but only with greatly expanded marine construction capacity. Building even 2,000 megawatts of offshore wind over the next five years will require a significant increase in the marine supply chain, according to Keith Hays, the consultancy’s research director.

Floating turbines can be assembled onshore and towed into position, making an end run around the offshore construction bottleneck. The platform that Blue H towed out of Brindisi Harbor in Puglia, Italy, this winter is called a tension-leg platform, a conventional offshore oil and gas platform design that floats below the surface, held rigidly in place by chains running to steel or concrete anchors on the seabed. Installed on top is an 80-kilowatt wind turbine fitted out with sensors to record the wave and wind forces experienced 10 kilometers offshore. Much bigger floating versions–2.5-megawatt and 3.5-megawatt turbines of the scale used in today’s offshore wind farms–are under construction by Blue H and could be installed as soon as this fall.

What’s unusual about Blue H’s design is the turbine’s two-bladed rotor–a design that lost out to the three-blade design in the 1990s as the wind-turbine industry scaled up. Martin Jakubowski, Blue H cofounder and chief technology officer, says that the noise and jarringly high rotation speeds that made two-bladers a loser on land are either irrelevant or a plus offshore. Faster rotation, meanwhile, offers two benefits. Jakubowski says that the 30-to-35-revolutions-per-minute frequency, twice that of a three-bladed turbine, is less susceptible to interference from the back-and-forth swing of the platform under wave action.